[Lynn Eades]

Richard has a good point about using a diesel oil in an older engine. I dont know the details of your engine and that's why I suggested you do some research. I run a "Total" brand diesel oil "Rubia "mono grade 30 which is designed for older engines. As it happens, I don't run a mechanical pump because I have seen some problems with old diaphragms and modern fuel, that have lead to oil dilution and run bearings. I also run a full flow oil filter in my cooler line.
The benefit of the high detergent oil is that once the engine is clean it will stay clean. I have run this oil from a major rebuild.
The Cummins Blue recommendation came from a study on the Ford Barn Forum and was the result of a study of various oils and their contents of various additive packages. The problem with modern (mainstream) petrol oils is they lack enough zinc to protect the cam and followers from premature failure.
Richard's "Classic 30" is good advice (not that I am judging him in any way) The "classic" bit covers the zinc issue. The straight 30 grade recommendation is about the greater ability of the mono grade to transfer heat. I too am an "A" grade mechanic of 50 years in the game, but I have probably done less engine work than him.